Contour enhanced images can be acquired by a scanning microscope using split detection (see, for example, T. Wilson and D. K. Hamilton, “Differential amplitude contrast imaging in the scanning optical microscope”, Applied Physics, B. 1983, pp. 187-191). In recent years, studies have been made to observe the morphology of the fundus in more detail by applying this technique to the scanning laser ophthalmoscopy (SLO) (see, for example, Yusufu N. Sulai, Drew Scoles, Zachary Harvey, and Alfredo Dubra, “Visualization of retinal vascular structure and perfusion with a nonconfocal adaptive optics scanning light ophthalmoscope”, J. Opt. Soc. Am. A 2014 pp. 569-579; Drew Scoles, Yusufu N. Sulai, Christopher S. Langlo, Gerald A. Fishman, Christine A. Curcio, Joseph Carroll, and Alfredo Dubra, “In vivo imaging of human cone photoreceptor inner segments”, IOVS. 14-14542, pp. 4244-4251; Ethan A Rossi, Kenichi Saito, Charles E. Granger, Koji Nozato, Qiang Yang, Tomoaki Kawakami, Jie Zhang, William Fischer, David R Williams, and Mina M Chung, “Adaptive optics imaging of putative cone inner segments within geographic atrophy lesions”, ARVO 2015).
The split detection method uses a peripheral light beam around the point image center area in the fundus conjugate point. The peripheral light beam is divided into a plurality of light beams. The arithmetic processing is performed by using the light beams to thereby obtain a phase contrast image of a different frequency band from that of a fundus conjugate point image. Such a split detection method is expected as a technology that allows the observation of the fundus tissues (especially, inner segment of photoreceptor cells) with no successful in vivo visualization heretofore.
In the conventional configuration, first, a light beam is separated into a light beam of the point image center area and a peripheral light beam around it by a light beam splitting element (e.g., annular mirror having an annular opening, etc.) arranged in a fundus conjugate point. The peripheral light beam is divided into a plurality of light beams by a light beam splitting element (e.g., edge mirror, etc.) arranged in a fundus conjugate point newly formed by an imaging optical system. Each of the light beams is received by a detector.
The light beam is required to be separated into the light beam of the point image center area and the peripheral light beam with high accuracy in the fundus conjugate point. However, since the point image size (Airy disk diameter) in the fundus conjugate point is several 10 μm to several 100 μm, a very high degree of accuracy is required to manufacture and install the light beam splitting element. As well as increasing the cost, it also increases the time required for alignment work.
In addition, with the use of the above-mentioned light beam splitting element, it is very difficult to change the number of divisions of the peripheral light beam. For example, to increase the number of divisions, it is necessary to newly form a fundus conjugate point. As a result, the long optical system and detectors provided as many as the number of divisions make it difficult to ensure the installation space. On the contrary, in some cases, the number of divisions is limited in relation to the installation space.
Further, in the conventional configuration, it is very difficult to change the division pattern, such as dividing direction of the peripheral light beam. For example, to change the dividing direction, highly accurate alignment work is newly required.